It has been known that halogen-containing organic polymers, especially the commercially important polyvinyl chloride polymers, are subject to deterioration and degradation when exposed to heat, light, and the weather. Various compounds and compositions have been proposed and utilized to stabilize these polymers. For the most part, such compounds have been directed primarily toward stabilization against the effects of heat such as that encountered during processing of the polymer and fabrication thereof into various articles.
A conventional method for making such mercaptides has been the reaction of a mercaptoacid ester with the chloride of the desired metal in the presence of a basic compound which is capable of removing hydrogen chloride as it is split out by the reactants in accordance with the equation: EQU (CH.sub.3).sub.2 SnCl.sub.2 +2HSCH.sub.2 (C.dbd.O)OC.sub.8 H.sub.17 +2NH.sub.4 OH .fwdarw.(CH.sub.3).sub.2 Sn(SCH.sub.2 (C.dbd.O)OC.sub.8 H.sub.17).sub.2 +2NH.sub.4 Cl+2H.sub.2 O
Ammonia or ammonium hydroxide has often been used because of its low cost. When the resulting mercaptide is a liquid, the ammonium salt may be washed away from it with water and then dried. When the mercaptide product is a solid at the usual working temperatures, however, the salt is more conveniently removed by filtration of the molten product. Disposal of the filter cakes from this sort of process is becoming more costly as regulations become stricter and the availability of landfills diminishes.
It is a widely held belief among those skilled in the art of stabilizing PVC compositions that some nitrogen compounds tend to promote the degradation of the polymer. Although it would have been advantageous from the standpoint of reducing wastes to allow the ammonium chloride to remain in the metal mercaptide or even to return some portion of the filter cake containing it to the filtered product, it has not been done until this invention because it was thought that the ammonium chloride would hurt the stability of PVC.